Can my station measure the QO-100 NB transponder LO stability?

Following a long discussion with Bernd Zoelgert DL2BZ about the frequency stability of the local oscillator of the QO-100 narrowband transponder, I have decided to try to measure the Allan deviation of the transponder. The focus here is on short-term stability, so we are concerned with observation intervals around \(\tau = 1 \mathrm{s}\).

Of course, as with any measurement problem, the performance of the measurement equipment should be better than the “device under test”. In this case, to measure the QO-100 LO it is necessary to compare it against a reference clock which is more stable (ideally an order of magnitude better).

My whole station is locked to a DF9NP GPSDO, which is a 10MHz VCTCXO disciplined by a uBlox LEA-4S GPS receiver. That’s great to measure long-term stability, but for short-term measurements you are essentially relying on the stability of the VCTCXO, which is not so great. Therefore, the whole purpose of this experiment is first to determine whether my station is actually able to measure the QO-100 LO or not. Spoiler: it turns out the answer is “no”, as in most articles whose title is phrased as a question.

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Using an external reference with the LimeSDR Mini

A while ago I spoke about feeding an external reference to the LimeSDR USB. Now I wanted to use an external reference with the LimeSDR Mini that I have in my QO-100 groundstation to lock all the system to GPS. Preferably I wanted to use 27MHz as the reference, since this is what I am using in my LNB, so this would save me from having to run 10MHz or another frequency to the groundstation.

I wasn’t so sure how well this would work, since there are a few threads with questions in the MiriadRF forums, but I haven’t seen any explaining things in a clear way. There are different anecdotes of things that worked or didn’t work for several people, but not that many definitive answers. Among all the threads, this one seems mostly helpful.

Somewhat surprisingly, everything has worked well on the first try. I am now using a 27MHz external reference with my LimeSDR Mini. Hopefully this post will be of help to other people.

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Second alpha for gr-satellites 3

Following the first alpha, I have released today v3-alpha1, the second alpha for gr-satellites 3. As I introduced in September, gr-satellites 3 will be a large refactor of gr-satellites, bringing many UI and under-the-hood changes. I am releasing a series of alphas during the development to get feedback from users. Each of the alphas focuses on a different aspect.

The second alpha is focused on input and output formats. New functionality has been implemented to allow the user to choose the input and output in a flexible way. This post describes the main features added.

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